How to measure the Samarinda coastal currents?

1. Location of Samarinda

Samarinda is a major city in the province of East Kalimantan, Indonesia. It sits on the banks of the Mahakam River and also opens onto the Makassar Strait.

The city has nurtured many cultures, such as Dayak, Bugis, and Javanese, in one big melting pot, each with their traditions and customs. This rich cultural heritage can be seen through the architectural and handicraft elements in this place.

It is part of Samarinda's identity-one of the vital ways of transportation and livelihood at the same time. Where it meets the sea, the river delta is a complex area that changes dynamically every year.

The sandy beaches face the Makassar Strait, mixed with mangrove forests. Mangroves have an essential ecological function. It gives protection to the coast through a natural barrier from erosion, generated by waves and storms. The roots of the mangroves provide a conducive habitat for an enormous amount of marine life, such as fish, crabs, and shellfish. The shallow waters surrounding the coast are full of nutrients because the mixing river-borne sediments with seawater support a diverse range of organisms.

The Makassar Strait is a wide body of water, providing both a heavy lane of shipping and a rich fishing ground. The bottom topography of the Strait around Samarinda is constituted for the most part by sand, coral reefs, and submarine slopes. The deeper areas of this strait serve as the setting for commercial shipping and large-scale fishing, whereas local fishing and recreational activities are significant in shallow areas.

2. What is the situation of the coastal currents near Samarinda?

Variations in coastal currents off Samarinda are influenced by more factors. The most influential factor could be monsoon winds. During southwest monsoon, the winds always push the surface waters in a certain direction and thus can bring warm and nutrient-rich waters from other areas. This can contribute to the higher productivity of the coastal marine ecosystem as it provides necessary nutrients for the growth of phytoplankton and other primary producers. The northeast monsoon, in turn, changes these current patterns and may advance cooler waters with different sediment loads.

The topography of the seabed is also very important. Currents can be deflected, accelerated, or slowed down by the presence of coral reefs, undersea ridges, and troughs. For example, over a coral reef, the general water flow can be deflected, and this produces areas of upwelling and downwelling. These latter areas are very important in the nutrient cycle, as they bring deeper, nutrient-rich waters to the surface, hence enabling a larger abundance of marine life to exist.

Another significant factor can be considered to be the input of freshwater from the Mahakam River. The large volume of freshwater discharge can significantly change the salinity of the coastal waters. The density difference that can cause different water masses and affect the vertical movement of the currents.

3. How to observe the coastal water flow of Samarinda?

Surface Drifting Buoy Method: Buoys are set in the water and let drift with currents. Their movements are monitored through satellite-based tracking systems. The path followed by the buoys can be used to identify the direction of the surface current and speed. This technique, however, mainly deals with the surface layer, which does not provide adequate details of currents within the different layers of water.

Anchored Ship Method: A ship is anchored within the coastal waters and current-measuring instruments are lowered from the ship into the water at different depths. This would allow measurement of the current characteristics at various levels. However, the ship itself may interfere with the natural flow of the water. This is not efficient for long continuous measurements.

Acoustic Doppler Current Profiler ​(ADCP) Method: ADCP current meter is one of the more advanced and handy techniques of measuring the coastal currents. It gives a detailed profile of the current velocities from the surface to a certain depth and thus allows one to get a more complete picture of the flow patterns within the water column.

4. How Do the ADCPs Using the Doppler Principle Work?

In general, the operation of ADCP current profiler is based on the Doppler effect. They shoot acoustic signals into the water. These acoustic pulses interact with moving particles in the water, like sediment particles and small organisms. Because the water is in motion, the frequency of the reflected pulses changes owing to the Doppler effect. This frequency shift is measured by the ADCP flow meter and calculates the velocity at different depths. It has multiple transducers facing in different directions that enable it to send and receive acoustic signals, which thus makes a measurement of the three-dimensional velocity structure of the water column possible.

5. What is required for high-quality measurement of Samarinda coastal currents?

The equipment has to be manufactured from such materials that are reliable for high-quality measurement of the coastal currents around Samarinda. It has to be resistant to the corrosive action of seawater and mechanical forces induced by waves and currents. A small size and light weight may be advantageous, as it makes deployment easier in a boat, buoy, or at the seabed.

The power consumption should be low because there are long-term measurements that are carried out in areas that are remote. It should have cost-effectiveness: the equipment should be as inexpensive as possible to carry out the large-scale measurement. The casing of the ADCP meter is made essentially from titanium alloy. The corrosion resistance is great, and the usage in the marine environment needs it the most. It is also strong and durable, able to resist the harsh marine conditions while being relatively lightweight.

6. How to Choose the right equipment for current measurement?

Application scenario: the choice of equipment for the current measurement near Samarinda depends on the application scenario. ADCP profiler installed on ships is suitable for ship-based measurements. It can be installed on the hull of the ship and can measure the currents when the ship is in a state of sailing or stationary.

A good choice to measure the currents near the bottom would be a bottom-sitting ADCP, which can sit on the seafloor and measure the current near the bottom with accuracy.

During floating applications, an ADCP mounted on a buoy would be appropriate. It can be fixed with a buoy to measure currents at depth while the buoy floats.

Frequency of ADCPs: 600kHz will work for most applications in water depths up to 70m, 300kHz is best in water up to 110m deep, and the longer-range 75kHz unit may be appropriate in water up to 1000m deep.

There are several well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a highly recommended Chinese ADCP brand is China Sonar PandaADCP. It is made of all - titanium alloy material, ensuring excellent performance and durability in the marine environment. It also offers an outstanding cost - performance ratio. You can find more information on its website: https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and moels.